340 
mass of boulders on the southern side of Loch Brandy, and clearly 
derived from the precipices which overhang the Loch on the three 
other sides, is advanced as another proof in favour of the glacial 
theory. It is impossible to conjecture, Mr. Lyell says, how these 
blocks could have been transported half a mile over a deep lake; but 
let it be imagined that the Loch was once occupied by a glacier, and 
the difficulty is removed. Loch Whorral, about a mile to the east 
of Loch Brandy, is also surrounded on its north, east and western. 
sides by precipices of gneiss, and presents on its southern an immense 
accumulation of boulders with other detritus, strewed over with 
angular blocks of gneiss, in some instances twenty feet in diameter. 
This moraine is several hundred yards wide, and exceeds twenty 
feet in depth, terminating at the borders of the plain of Clova in a 
multitude of hillocks and ridges much resembling in shape some 
terminal moraines examined by Mr. Lyell in Switzerland. 
The great transverse barrier at Glenairn, where the valley of the 
South Esk contracts from a mile to half a mile in breadth, and is 
flanked by steep mountains, Mr. Lyell formerly regarded as very 
difficult of explanation, Seen from below, this barrier resembles an 
artificial dam 200 feet high, with numerous hillocks on its summit. 
On the eastern side it appears to have been denuded to the extent 
of about 300 yards by the Esk. Its breadth from north to south 
is about half a mile. The lower part, 30 feet in depth, laid open 
in the river cliff, consists of impervious, unstratified mud, full of 
boulders; but the total vertical thickness of this deposit is stated to 
be from 50 to 80 feet; and the upper part of the barrier is com- 
posed of from 50 to 100 feet of very fine stratified materials. It is 
not possible, Mr. Lyell observes, to account for the accumulation of 
this barrier by the agency of water, particularly as no tributary 
joins the Esk at this point; but if the barrier be supposed to be the 
large terminal moraine of a receding glacier, then its form and 
position, he says, are easily to be understood. M. Agassiz, in his 
work on glaciers, shows, that when these masses of ice enter a nar- 
row defile from a broader valley, the lateral moraines are forced 
towards the centre, and the mass of transported matter is spread 
more uniformly over the whole. Such a terminal moraine left by a 
receding glacier in a defile, Mr. Lyell states, would dam back the 
waters of the glacier, and produce a lake; and the phenomena pre- 
sented by the barrier of Glenairn, and the plain which extends in 
its rear, are fully explicable on the assumption of their having been 
produced by a glacier. The stratification of the upper portion of 
the barrier is also shown to be partly in accordance with the effects 
produced by the formation of ponds of water on the surface of mo- 
raines; but Mr. Lyell states, that the accumulation of so great a 
capping of stratified. materials is still the most obscure character of 
the deposits under consideration. 
At Cortachie, about four miles below the barrier of Glenairn, the 
South Esk enters-the country of old red sandstone, and a mile and 
a half lower it is jomed by the Proson, and a mile yet lower by the 
Carity. In the district in which these streams unite there is a con- 
